Method of coating



United States Patent 3,498,820 METHOD OF COATING Frederick E. Hawkins,Ambler, Pa., assignor to Certain- Teed Products Corporation, Ardmore,Pa, a corporation of Maryland No Drawing. Filed Nov. 7, 1966, Ser. No.592,305 Int. Cl. B05c 7/08; B44d 1/44 US. Cl. 11754 7 Claims ABSTRACT OFTHE DISCLOSURE A method is disclosed for applying a heat hardenableliquid coating composition to the interior surface of an asbestos-cementpipe including heating the pipe to a temperature of at least about 220F., maintaining the temperature of the pipe in excess of about 220 F.for a relatively short period of time, for example one rrrinute to threehundred minutes and cooling the pipe by at least about F. A heathardenable liquid coating composition is then applied to the interiorsurface of the pipe as it is rotated about its longitudinal axis, therotation being continued until the coating composition forms a sag-freelining.

This invention relates to coating the interior surface of a pipe orother open-ended hollow object with a heat hardenable liquid coatingcomposition and more particularly to a method for heat treating anasbestos-cement pipe prior to coating the interior surface thereof witha heat hardenable liquid coating composition.

Heretofore it has been proposed to line or coat the interior surface ofasbestos-cement pipes with fluid impervious and chemically inertlinings. The purpose of the lining is to protect the pipe from beingdegraded by corrosive fluids which flow through the pipe. In cases wherethe interior surface of the pipe must be cleaned from time to time, thelining permits the use of acid cleaners thereby facilitating removal ofdeposits, whereas, such acid cleaners would degrade part of theasbestos-cement composition if the pipe were not lined. To form a fluidimpervious protective barrier and one that does not hinder the flow offluids through the pipe, the lining should adhere firmly to the wall, befree of sags, ripples, pinholes, blisters and other surface defects andbe of suflicient thickness to cover minor irregularities on the surfaceof the pipe.

Whereas there have been developed and made available various coatingmaterials which are chemically resistant and fluid impervious, theapplication of such materials at high production rates to the interiorsurface of the pipe to form thereon a smooth lining free of surfacedefects and irregularities remains a problem. Such coating materials areapplied generally in liquid form to the interior surface of the pipe byspraying the liquid thereon as the pipe is rotated about itslongitudinal axis at a speed high enough to spread the coating materialover the entire surface of the pipe. After the liquid coating materialis applied, the rotation of the pipe is continued until the liquid layerof coating material hardens to the extent that it will not flow or sagwhen rotation is stopped.

Typical of the problems associated with the application at highproduction rates of liquid coating materials to the interior surface ofthe pipe are those encountered when applying a liquid epoxy resincoating composition, a coating material in common use and one which uponhardening becomes a fluid impervious and chemically inert substance. Theliquid epoxy coating composition can be made up in the form of asolution of solid epoxy resin dissolved in a suitable volatile solventor in the form of a mixture of a liquid epoxy resin and hardener whichmixture may also contain an accelerator. Prob- 3,498,820 Patented Mar.3, 1970 ice lems are encountered when either of these types ofcompositions are applied.

It has been found that if a solution of epoxy resin and volatile solventis applied to the interior surface of a rofating pipe by spraying thesolution thereon, it is virtually impossible to obtain a lining that isfree of blisters, pinholes or other surface defects. This is because thethickness of the lining that can be applied upon one pass of thespraying apparatus is limited by the need to have the lining thin enoughto permit the evaporation of the solvent from the surface of the lining.Applying a second coating of a solution reduces somewhat the number ofsurface defects but by no means insures the formation of a fluidimpervious lining.

With respect to coating compositions comprised of a liquid epoxy resin,hardener and accelerator, it has been found that the various types ofhardeners and accelerators that are available have different effects onthe time it takes for the layer of coating to solidify to a sag-freestate and the quality of lining formed.

Liquid epoxy resin compositions which contain hardeners and acceleratorsthat are effective in solidifying at room temperature to a sag-freestate in a relatively short period of time form linings which are notimpervious to water, alkali, or acids. The desired chemical resistanceof the lining can be attained by not rising such hardeners andaccelerators, but such compositions when applied to the pipe at ambienttemperature form linings which do not reach a sag-free state until thepassage of an excessively long period of time, for example, one hour.During this period of time, the pipe must be rotated about itslongitudinal axis at a speed high enough to develop suflicientcentrifugal force to maintain the hardening liquid lining sag free. Theutilization of such types of compositions creates a bottleneck in theproduction process. Another disadvantage of such compositions is thatthe lining while in a state of hardening often develops a permanentblush which detracts from the appearance of the pipe.

The solidifying of liquid epoxy coating compositions which are slowreacting at ambient temperature can be accelerated by applying thecomposition of a heated pipe. The heat transferred from the pipe to thecomposition accelerates the hardening reaction. However, it has beenfound that if the liquid composition is applied to a pipe having atemperature of about F., blisters and pinholes are formed in the liningwith the result that the lining is defective. Temperatures greater thanabout 120 F. cause an increase in the number of blisters that are formedand it is at these temperatures where the hardening is accelerated to asatisfactory degree. It is believed that the blisters are caused byexpanding gases, particularly water vapor, within the pores of the pipewall, the expansion of the gases being triggered by the heat of thepipe. It is also theorized that the heat of the pipe causes watertrapped within the inner body portions of the asbestos-cementcomposition to move toward the interior surface of the pipe Wall andcontribute to blister formation.

A method has heretofore been proposed whereby the heat of a hot pipe canbe utilized to speed up the hardening of the liquid coating compositionwhile avoiding the blister and pinhole formation problem. This methodgenerally consists of applying to a heated pipe a liquid resin coatingcomposition which has substantially the same temperature as the pipewhile maintaining the outside of the pipe wall in a state of cooling.However, it has been found that this method cannot be relied upon toavoid consisently the blister and pinhole formation problem. Inaddition, this method has other disadvantages. For example, it isreported that when coating the interior surface of a pipe that has awall thickness of greater than about 2 inches, it is necessary toprovide additional equipment for cooling the outside of the pipe suchas, for example, equipment for spraying water on the exterior pipe wall.Another disadvantage of this method is that if the coating has beenapplied to a pipe which has a temperature above 212 B, it is necessarythat the moisture within the pipe wall be driven off before the liquidcoating composition is applied. This necessitates that the pipe be driedfor long periods of time at high temperatures, e.g., as much as 16 hoursat 240 F. From a production standpoint, such drying procedure isintolerable and consequently the utilization of temperatures above 212P. where the coating composition hardens at advantageously fast ratesare generally avoided.

Thus, according to known methods, it is not possible to consistentlyform high quality linings at high production rates on the interiorsurface of an asbestos-cement pipe by applying thereto compositionscomprised of liquid epoxy resins and hardeners, such compositions beingreferred to hereinafter as heat-hardenable liquid-coating compositions.

It is therefore an object of this invention to provide an improvedmethod for applying heat-hardenable liquidcoating compositions to theinterior surface of a pipe or other open-ended, hollow object.

It is an additional object of this invention to provide an improvedmethod for applying a heat-hardenable liquid-coating composition to theinterior surface of a heated asbestos-cement pipe to form thereon asmooth lining which is free of blisters and other surface defects.

It is still another object of this invention to provide an improvedmethod for coating the interior surface of a heated asbestos-cement pipeby applying thereto a heathardenable liquid coating which solidifies toprovide a smooth blister-free lining without having to dry the pipebefore application of the coating.

In accordance with this invention, the above objects are attained byfirst heating the pipe to a high temperature for a relatively shortperiod of time, cooling the pipe somewhat and then substantiallyimmediately after the cooling applying a heat-hardenable liquid-coatingcomposition to the interior surface of the hot pipe.

This invention is primarly directed to heat treating an asbestos-cementpipe or other open-ended hollow fibrocement object which has been cured,for example by high pressure steam curing, but which, nevertheless,still contains water within the walls or body portions of the objectwhich tends to move toward the interior surface of the wall when theobject is heated to temperatures of about 120 F. and above. Generally,the amount of water within the walls of the pipe may be anywhere fromabout 4 to percent by weight of the pipe. Asbestos-cement pipes normallycontain from about 4 to 7 percent by weight of water which has notentered into the hydration reaction. Additional amounts of water may bepicked up by the pipe from the atmosphere. In cases where the pipe isstored outside and exposed to rain, it is not unusual for the pipe tocontain as much as 15 or more percent by weight of water.

More specifically, this invention provides a method for treating anasbestos-cement pipe or other open-ended hollow fibro-cement objectsprior to coating the interior surface thereof -'with a heat-hardenableliquid-coating composition comprising providing a cured open-endedhollow fibro-cement object having water within the wall of the object,heating the innermost body portions of said object to a temperaturewithin on initial temperature range to raise the temperature of saidbody portions to at least about 220 F., maintaining the temperature ofsaid body portions within said initial temperature range for a period oftime substantially less than it takes the heat to completely dry theobject, and cooling said body portions to a temperature within a secondtemperature range to lower the temperature of the body portions by atleast about 15 Fahrenheit degrees and preferably by at least aboutFahrenheit degrees thereby readying the object for the substantiallyimmediate application of a heat-hardenable liquid-coating composition tothe interior surface thereof.

By utilizing the method set forth above it is possible to applyheat-hardenable liquid-coating compositions to heated asbestos-cementpipes or similar objects and obtain smooth linings free of pinholes andblisters and other surface defects while avoiding the problems attendantwith and inherent in known methods for coating.

As mentioned hereinabove, one of the major problems encountered withpracticing hertofore known methods of coating is that theasbestos-cement pipe must be heated for inordinately long periods oftime to completely dry the pipe before the heat-hardenable liquidcoating can be applied to a hot pipe in order to obtain linings that arefree of blisters and pinholes. As explained above, the cause of theblister and pinhole formation is attributable to water moving toward thepipe surface. The purpose of the drying therefore is to drive off all ofthe water and therefore rid the pipe of the blister, pinhole inducer. Ithas now unexpectedly been found that it is not necessary to drycompletely the pipe in order to avoid blister and pinhole formation in alayer of liquid coating applied to a hot pipe. By following the methodof this invention, much time can be saved and high quality linings canbe provided if the temperature of the innermost body portions of thepipe is raised to above about 220 F. and maintained at such temperaturefor relatively a short period of time, lowering the temperature by atleast about 15 F. and applying a heat-hardenable liquidcoatingcomposition, for example, a liquid epoxy-resin hardener composition, tothe interior surface of the pipe shortly after the cooling has beeneffected.

Thus, in accordance with this invention a heat-hardenable liquid coatingcomposition can be applied to the interior surface of an asbestos-cementpipe by first heating the pipe to raise the temperature of its innermostbody portions to at least 220 F. and preferably higher, maintaining thetemperature of said body portions at about 220 F. or higher for a periodof time substantially less than it takes for the heat to drive off allof the water from within the pipe walls, cooling the pipe to lower thetemperature of the body portions by at least about 15 F. but not to anextent that there will not be suflicient heat within the pipe walls toaccelerate the hardening of the coating composition, rotating the cooledbut still hot pipe about its longitudinal axis and then applying to theinterior surface of the pipe a heat-hardenable liquid-coatingcomposition by any conventional means, for example, by spraying. Havingapplied the layer of coating, rotation of the pipe should be continuedfor at least a period of time until the coating material has hardened tothe extent that the layer of coating will not sag when rotation isstopped.

In accordance with this invention, the asbestos-cement pipe or similarobject can be heated by any suitable equipment, for example a tunnelthrough which hot air is circulated to raise the temperature of theinnermost wall portions of the pipe to about 220 F. or higher.Preferably the pipe should be heated to a temperature falling within therange of about 220 F. to 300 F. It should be understood, however, thathigher temperatures can be used. The time that the pipe is maintainedwithin this temperature range or at least above 220 P. will varydepending on the temperature of the pipe and the wall thickness of thepipe. In general, pipes having a wall thickness of from about a fractionof an inch, for example, one-third of an inch to about a couple ofinches which have been heated to a temperature within the range of 220F. to 300 F. should be maintained at a temperature within said range forabout 1 to 300 minutes, the thicker Walled pipes generally beingmaintained within this temperature range for the longer periods of time.The moisture content of the pipe will also influence the temperature towhich it is heated and maintained thereat.

For the same temperature, pipes with greater amounts of water should bemaintained at the temperature for longer periods of time than pipes withlower amounts of water. Pipes with the higher water content should beheated to higher temperatures than pipes with lower water content if thetime at which the pipes are maintained at their respective temperatureis about the same. The temperature of the pipe may be maintained withinthe above time period for longer periods of time but to no realadvantage and as such it is unnecessary. The advantage of utilizing themethod of this invention is evident when considering that it wouldgenerally takeanywhere from to 48 hours to completely dry a pipe heatedto a temperature within this range, the time depending on temperature,water content and wall thickness of the pipe.

Having heated the pipe as above described, its temperature should thenbe lowered by at least about F. and preferably F. The cooling may beaccomplished with any suitable equipment, for example, a tunnel throughwhich hot air is circulated, i.e., air which is heated but is at a lowertemperature than the temperature it is desired to cool the pipe. It isadvantageous from a production standpoint that the pipe be cooled asfast as possible. Pipes having a wall thickness of about a fraction ofan inch, for example, one-third of an inch to about a couple of inchescan be cooled to a temperature within the range of about 180 F. to 205F. in a tunnel through which air at about 150 F. to 180 F. is circulatedin about 10 to 100 minutes. It should be understood that other means canbe utilized which will reduce the temperature of the pipe more quickly.

The number of degrees the temperature of the pipe is lowered will dependon a number of factors.

In this respect, the characteristics of the coating composition beingapplied must be taken into consideration. The temperature of the pipeafter cooling should be hot enough to promote setting of the coatingcomposition within a reasonable time, for example 5 to 10 minutes andthus the setting characteristics of the composition will influence thetemperature to which the pipe is lowered. On the other hand, thetemperature of the pipe after cooling must not be so hot that the heattransferred from the pipe to the coating composition Will cause thecomposition to bubble and thereby form blisters and pinholes. In thisregard, it is pointed out that the setting of some liquid coatingcompositions, for example, epoxy compositions, is an exothermic reactionthereby contributing heat build-up in the lining being applied, whichheat build-up will raise the temperature of the coating compositionabove the temperature of the pipe and this may be sufficient to causebubbling of the composition.

When epoxy-resin compositions (described more fully below) are utilized,it is preferred that the temperature of the pipe be within the range ofabout 180 F. to 205 F. when the coating is applied. The heat of the pipeat such temperatures is effectively used to accelerate the hardeningreaction and does not cause the composition to bubble.

The number of degrees that the pipe is lowered will also depend on themoisture content of the pipe and the temperature to which it has beenraised initially. Pipes with the higher moisture content which have beenheated to temperature of about 250 F. to 300 F. or higher should havetheir tempreatures reduced by substantially more than 20 F., forexample, by about 50 F-100 F. or even more.

The method of this invention can be used to good advantage to improveany coating process wherein a heathardenable liquid-coating compositionis applied to the interior surface of a heated asbestos-cement pipe orsimilar object and wherein the layer of coating composition has atendency to have blisters or pinholes formed therein due to water orgases being given off from the interior surface due to heat. Exemplaryof the kinds of liquid-coating compositions that can be used arecompositions comprised of either polyurethane, polyester, or epoxyliquid coating resins, the last mentioned being preferred.

Such preferred coating materials are those epoxy-based compositionswhich upon curing adhere firmly to the interior surface of the pipe, areresistant to chemical attack by neutral, acidic, or alkaline fluids, andwhich have low absorbency for water and aqueous solutions of acids oralkali. Generally, such compositions will be comprised of 55 to percentof a mixture of epoxy resin and hardener with the ratio of epoxy resinto hardener being approximately stoichiometric and 15 to 45 percentsilica.

Particular epoxy resins that can be used to good advantage in thepractice of this invention are those diglycidyl ethers of bis-phenol Athat have viscosities of the general order of 10,000 to 16,000centipoise at 77 F. and that have an epoxide equivalent in the range ofabout 175 to 200. Such epoxy resins are readily available andidentifiable in the trade as Jones Dabney Epi Rez 510, Ciba Araldite9001, Shell Epon 828, Union Carbide Bria-2600, Bria-2400, and Erla-2774,and Reichhold Epotuf 6140.

Examples of hardeners that can be used in the coating compositions arediethylenetriamine and triethylenetetramine, the last-mentioned being apreferred hardener. The amount of hardener admixed with the epoxy resinpreferably should be the stoichiometric amount needed to react with theresin to give the requisite chemical resistance. For best results afreshly prepared mixture of the epoxy coating composition containing ahardener should be applied to said surface substantially immediatelyafter the components have been thoroughly mixed. The reason for this isthat if too much time elapses between the mixing of the epoxy and thehardener, the coating composition will begin to set, and thereby preventuniform distribution of the composition over the surface to be coated.Another disadvantage resulting from allowing the composition toprematurely set is that it will tend to stick to the coating equipmentand prevent uniform flow of the composition through the equipment andperhaps even block it.

In addition to the epoxy resin and hardener, other components can beincluded in the coating composition. For example, it is expedient to addfinely pulverized silica, for example, 15 micron silica, to thecomposition. Any silica that is readily dispersible in the uncured epoxycomposition can be employed. The silica functions to extend thecomposition, has the property of slowing down the reaction between thehardener and the epoxy resin thereby aiding in controlling and handlingthe liquid composition, reduces shrinkage as the epoxy hardens and alsoreduces the water adsorption capacity of the plastic lining.

Other ingredients which can be added to the composition includepigments, inert extenders and reactive materials such as, for example,triphenyl phosphite.

The epoxy compositions described above can be at room temperature whenapplied to the pipe; however, the compositions which at room temperatureare relatively thick viscous liquids should be heated so that they willflow more readily during application. Generally the viscous compositionsshould be heated to a temperature within the range of about F. to 155 F.and preferably about F. to F.

Substantially immediately after cooling the heated pipe by at leastabout 15 F., a suitable coating material such as, for example, an epoxycomposition of the kind described above, is applied to the interiorsurface of the pipe by spraying or other appropriate means. In order touniformly distribute the coating material on the interior of the pipeand to maintain such distribution until a sagfree lining is formed, itis desirable to rotate the pipe about its longitudinal axis while theliquid coating is being applied. Preferably the longitudinal axis isaligned in a substantially horizontal plane and the pipe rotated withoutbouncing. The rotation should be continued until the coating compositionhas hardened to a state where it will not sag when the rotation isstopped.

The examples appearing below serve to illustrate the practice of thisinvention.

In each of the examples the temperature of the pipe wall is thetemperature of the innermost portions of the wall as measured by one ormore thermocouples buried in the Wall. The amounts of the componentswhich cornprise the coating composition are given in parts by weight.

EXAMPLE I An asbestos-cement pipe having an inside diameter of 5.85inches and a wall thickness of 0.66 inch was heated in an oven until thewall reached a temperaturev of about 275 F. The pipe was maintained at atemperature in the neighborhood of 275 F. for about 44 minutes. The pipewas then transferred to an oven which had a temperature of about 190 F.and after about 23 minutes the temperature of the pipe wall had cooledto about 205 F. The heated pipe was removed from the oven and rotatedabout its cylindrical axis at a speed of about 200 revolutions perminute and there was applied to the interior surface of the rotatingpipe a liquid coating composition comprised of 100 parts of Jones DabneyEpi Rez 510 epoxy resin, 12 parts of triethylenetetramine hardener and60.4 parts of 15 micron silica. The composition was heated to atemperature of about 120 F. and applied to the interior surface of therotating pipe along its entire length within about one minute after thepipe had been cooled to about 205 F. After applying the composition,rotation of the pipe was continued for a few minutes longer at whichtime the composition had hardened to the extent that the layer ofcoating did not flow or sag when rotation was stopped. There was thusobtained a lining having a uniform thickness of about mils which wasfree of sags, ripples, pinholes, blisters and other surfaceirregularities.

EXAMPLE II An asbesto-cement pipe of the kind described in Example I washeated in an oven until the wall reached the temperature of 220 F.Immediately after reaching 220 F., the pipe was cooled within about 10minutes to a temperature of about 207 F. The heated pipe was thenrotated about its cylindrical axis at a speed of about 485 revolutionsper minute and lined with a liquid-coating composition comprised of 68parts of Jones Dabney Epi- Rez 510 epoxy resin, 7.14 parts ofdiethylenetriamine hardener and 32 parts of 10 micron silica. Thecomposition which was at room temperature was applied to the interiorsurface of the rotating pipe along its entire length within about oneminute after the pipe had been cooled to 207 F. After applying thecomposition, the speed of rotation of the pipe was reduced to 216revolutions per minute and rotation of the pipe was continued at thisspeed for about five minutes. The lining thus obtained was slightlytacky but did not run or sag and was free of blisters, pinholes andother surface defects or irregularities. The lining had a thickness ofabout 12 mils.

EXAMPLE III 8 inches and a wall thickness of 0.57 inch was heated in anoven until the wall reached the temperature of about 220 F. Immedaitelyafter reaching this temperature, the pipe was then cooled to atemperature of between about 187 F. and 201 F. over a period of about 10minutes and upon reaching this temperature was rotated about itscylindrical axis at a speed of about 400 revolutions per minute. Acoating composition at room temperature comprised of 52.7 parts of ShellEpon 828 liquid epoxy resin, 13.2 parts of triphenylphosphite, 4.1 partsof diethylenetriamine hardener and parts of 10 micron silica was appliedto the interior surface of the rotating pipe along its entire lengthwithin about one minute after the pipe had been cooled to saidtemperature. After applying the coating, the rotation of the pipe wasslowed to 200 revolutions per minute and rotation at this speed Wascontinued for five minutes after which a smooth lining free of blisters,pinholes or bubbles and having a thickness of 12 mils was obtained.

EXAMPLE IV An asbestos-cement pipe having an inside diameter of 5.85inches and a wall thickness of 0.72 inch was heated in an oven until thewall reached the temperature of about 270 F. The pipe was maintained ata temperature of within the range of 220 F. to 270 F. for about 30minutes, The pipe was then cooled over a period of time of about 10minutes to a temperature of 190 F. to 196 F. Immediately after the pipewas cooled to said temperature, it was rotated about its cylindricalaxis at a speed of about 200 revolutions per minute and there wasapplied a coating composition having a temperature of 116 F. andcomprised of parts Union Carbide Erla 2772 epox resin, 12 parts oftriphenylphosphite, 10.8 parts of triethylenetetramine hardener and 53.7parts of silica to the interior surface of the rotating pipe along itsentire length. After applying the composition, rotation of the pipe wascontinued for a few minutes longer at which time the composition hadhardened to the extent that the layer of coating did not flow or sagwhen rotation was stopped. There was thus obtained a lining having auniform thickness of about 15 mils which was free of sags, ripples,pinholes, blisters, and other surface irregularities, Following the sameprocedure, good quality linings having thicknesses of 23.5 mils and 40mils were also made.

I claim:

1. In the process of lining a heated asbestos-cement pipe wherein aheat-hardenable liquid-coating composition is applied to the interiorsurface of the hot pipe as the pipe is being rotated about itslongitudinal axis the improvement which comprises heating the pipe toraise the temperature of its innermost body portions to at least 220 F.,maintaining the temperature of said body portions above about 220 F. fora period of time ranging from about 1 minute to about 300 minutes,cooling the pipe to lower the temperature of said body portions by atleast about 15 F., and as the hot pipe is at said lower temperature,rotating the pipe and applying to the interior surface thereof aheat-hardenable liquid-coating composition.

2. A method according to claim 1 wherein the pipe is cooled to atemperature ranging from about 180 F. to about 205 F., wherein thecoating composition is comprised of an epoxy-resin coating and ahardener and wherein the composition as it is appliedto the interiorsurface of the pipe is at a temperature between about F. and about F.

3. A method for coating the interior surface of an asbestos-cement pipeor other open-ended hollow fibrocement object with a heat-hardenableliquid-coating composition comprising providing a cured open-ended hollow fibre-cement object having water contained within the wall of theobject, heating the innermost body portions of said wall to atemperature within an initial temperature range to raise the temperatureof said body portions to at least 220 F., maintaining the temperature ofsaid body portions within said initial temperature range for a period oftime substantially less than it takes the heat to completely dry theobject, and cooling the said body portions to a temperature within asecond temperture range to lower the temperature of the body portions byat least about 15 F. thereby readying the object for the substantiallyimmediately application of a heat-hardenable liquid-coating compositionto the interior surface thereof, the temperature within said secondtemperature range being sufliciently high to promote the setting of saidcomposition when it is applied to said interior surface and applying theheat-hardenable liquid-coating composition to the interior surface ofthe object,

4. A method according to claim 3 wherein the body portions are cooled byat least about 20 F.

5. A method according to claim 3 wherein the initial temperature range,the period of time at which said body portions are maintained withinsaid initial temperature range and the second temperature range areinterrelated so that upon application of the composition to the interiorsurface of the object, the heat of the object will accelerate hardeningof the composition to the extent that a smooth sag-free, bubble-freelining will be formed within a period of time of less than about 10minutes.

6. A method according to claim 5 wherein the said composition iscomprised of an epoxy resin coating and a hardener and wherein saidsecond temperature range is about 180 F. to 205 F.

7. A process for lining the interior surface of an asbestos-cement pipewith a heat-hardenable epoxy liquidcoating composition which comprisesproviding a cured asbestos-cement pipe having moisture within the pipewalls, heating the pipe to a temperature higher than about 220 F.,maintaining the temperature of the pipe above about 220 F. for a periodof time less than it takes the heat to completely dry the pipe, and thencooling the pipe to a temperature Within the range of about 180 F. toabout 205 F., and as the temperature of the pipe is in said lowertemperature range, rotating the pipe about its longitudinal axis andapplying to the interior surface of the rotating pipe an epoxyliquid-coating composition comprised of an epoxy resin coating and ahardener, said composition having a temperature between about F. andabout F. to form on said surface a smooth, uniform thickness, layercoating composition free of blisters, pinholes and other defects, andcontinuing the rotation of the pipe until the resin has hardened to theextent that said smooth layer of coating will not sag when rotation isstopped.

References Cited UNITED STATES PATENTS 2,778,283 1/1957 Bettoli.3,219,472 11/1965 Hucks 11747 ALFRED L. LEAVITT, Primary Examiner C. R.WILSON, Assistant Examiner US. Cl. X.R. l17-95

